This map shows the top ten credit card issuers, their state of charter (except for AmEx and Capital One that are not nationally chartered), and the maximum interest percentage cap for credit cards.

These clusters were largely formed by a 1978 Supreme Court decision (Marquette National Bank v. First of Omaha Service Corp.) that determined national banks only have to obey the interest-rate caps of the state they are chartered in, not that of the state where a bank's customer lives. This means that when a bank from a state without limits on interest, like Delaware, issues credit cards to people living in states like Minnesota, which caps credit card interest at 18 percent, the customer can be charged any rate of interest.